This invention relates to magnetrons.
In one known magnetron design, a central cylindrical cathode is surrounded by an anode structure which typically comprises a conductive cylinder supporting a plurality of anode vanes extending inwardly from its interior surface. During operation, a magnetic field is applied in a direction parallel to the longitudinal axis of the cylindrical structure and, in combination with the electrical field between the cathode and anode, acts on electrons emitted by the cathode, resulting in resonances occurring and the generation of r,f energy. A magnetron is capable of supporting several modes of oscillation depending on the coupling between the cavities defined by the anode vanes, giving variations in the output frequency and power. The mode of operation which is usually required is the so-called pi mode of operation.
It is desirable to be able to suppress the transmission of power generated in certain modes, for example, the so-called pi−1 mode. It has been discovered that power generated in this mode, if transmitted, may interfere with other electronic devices such as mobile phones, satellite links and other communication systems. Various methods have been proposed to suppress this mode of operation but these have generally been found to be costly, complicated, and also to suppress radiation in desired modes of operation, for example the pi mode. The invention arose from work relating to magnetrons for marine radar applications. Such magnetrons are small, simple and low cost devices and therefore a low cost and straightforward solution to the problem of pi-I radiation was sought.